If you’re stranded at sea, surrounded by water, drinking it seems like a no-brainer, right? Wrong! Seawater is four times saltier than your blood, and drinking it will dehydrate you faster than the sun beating down on that lifeboat. But if we can’t drink it, how do we turn it into freshwater?

Humans have been desalinating seawater for thousands of years, and today, 17,000 desalination plants provide drinking water for millions. But the process isn’t perfect—thermal desalination requires a lot of energy (often from fossil fuels), and reverse osmosis, while more efficient, still has costs and waste issues.

As water scarcity looms for 87 countries by 2050, the need for sustainable solutions is greater than ever. Could renewable-powered desalination or even wastewater recycling be the key? Watch the video from Ted Ed below to dive into the science of turning saltwater into survival water!